Tuesday, December 30, 2014

Evolution
is often cited as the core of biology but it has also been exhausted in various
media outlets from television to newspapers and books. One very popular
children’s television program, Pokémon, shows many of the organisms known as Pokémon
“evolving” into different forms which acquire a wide array of new abilities
that make them more successful than their previous forms. Understandably, much
of the actual scientific meaning of evolution is lost in the show, but the
concept of turning into a new form with new abilities often holds true in
science. In this sense, the way the Pokémon “evolve” into another form is
actually a metamorphosis rather than evolution as is known in the scientific
context. One prime example, Giardia
lamblia, also known as Giardia
intestinallis or Giardia duodenalis,
is a protozoan whose human infection life cycle revolves around the metamorphosis
from the cyst form into the trophozoite form (Figure 1).

G. lamblia was first discovered in the
seventeenth century and became relevant in the United States and Europe in the
1960s and 1970s (2). Transmission often occurs by ingesting food or water
contaminated with G. lamblia cysts
but can also spread directly through the fecal-oral pathway which is
characteristic of poor hygiene practices (2). One very unique feature of giardiasis,
or the infection with G. lamblia, is that
the infectious G. lamblia
trophozoites are confined strictly to the lumen of the small intestine which does
not spread to the blood stream like many other protozoan infections (1). Due to
the specific localization of this infection to the small intestine, the major symptoms
associated with giardiasis include severe, watery diarrhea and stomach cramps. It
is now cited as the leading cause for waterborne diarrhea in the United States
(2). Approximately 5,000 people are hospitalized annually in the US and
millions of cases are reported world-wide (2). One of the most effective
medications against giardiasis is metronidazole, which is a nitroimidaozole antibiotic
medication (2). One of the key elements of this drug and how it avoids harming
human cells, is that it attacks the anaerobic pathways in G. lamblia which are essential for the protozoan’s survival. In
giardiasis, this drug ultimately damages the DNA of the infectious trophozoite
stage of infection and kills the protozoan before it completes its life cycle
and damages the host.

The life cycle of G. lamblia can be split into two distinct phases; the dormant, cyst
phase and the infectious, trophozoite phase. The cysts of G. lamblia have been shown to be extremely resilient to a wide
variety of environmental conditions and also have a metabolic rate of just ten
to twenty percent of the trophozoite form allowing them to survive for extended
periods outside of their hosts. This begs the question as to how the cyst form
of G. lamblia “evolves” into the
trophozoite form so quickly in the human host intestine. The first step in
human infection is ingesting the resilient cysts (only 10 required for
infection) through contaminated water or food as stated above (2). Thereafter,
the cysts have to travel through the digestive tract, avoiding degradation till
they reach the small intestine. There have been several studies regarding the metamorphosis
phenomenon which have found that the shift in pH from the acidic stomach to the
slightly alkaline pH of the small intestine serves as a signal to alter the
morphology and gene expression of the cyst which results in the formation of
trophozoites (4). Hetsko et. al. found that it was likely that there was
pre-made mRNA ready to be translated
when the cysts were exposed to the varying physiological pH transitions, which
may encode for a variety of surface proteins such as adhesive molecules for
localization in the small intestine (4). This “evolution” of the cyst form of G. lamblia to the trophozoite is termed
excystation or encystation depending on the stage of infection (Figure 1).

After “evolving” into the infectious
trophozoite form due to the various pH signals in the digestive tract, they start
causing symptoms in individuals by localizing to the duodenum and the upper
intestine (2). Symptoms such as watery diarrhea, excessive flatulence, greasy
stools, stomach cramps, and bloating are some of the most common symptoms
associated with giardiasis (1). However, it should be noted that giardiasis can
be asymptomatic in people with strong immune systems and usually causes very severe
symptoms only in immunocompromised individuals. It is hypothesized that the
colonization of G. lamblia in the
small intestine results in disease due to a variety of mechanisms such as: by
the direct damage of the human intestinal mucosa, through the release of
cytopathic substances from the trophozoites, and/or that an immune response that
results in theinflammation of the mucosa
cells (2)(3). Finally the trophozoites’ extended stay in an alkaline pH in the
small intestine also serves as a signal for the encystation process which triggers
metamorphosis back into the dormant cyst form which are excreted through the
large intestine and ultimately in the feces circling back to the first stage of
the G. lamblia life cycle (2)(4).

Just as Pokémon “evolve” into different
forms with different characteristics, Giardia
lamblia metamorphoses from its dormant, cyst form to an infectious,
trophozoite form by sensing sudden physiological pH changes seen in the
digestive tract. This metamorphosis event is vital for the protozoa to cause
disease in humans and ultimately complete its life cycle. Further understanding
of this mechanism of metamorphosis can be vital in furthering treatment and
prevention of this disease.

Monday, December 29, 2014

Suppose
you are on a summer vacation to Florida when you decide to visit the beautiful
blue waters of the Atlantic Ocean. Upon your arrival you are alarmed to find the
water is not blue at all but instead its bright red! For someone who has never
witnessed a Florida red tide this phenomenon would undoubtedly cause some concerns
and for good reason. Florida red tides are also known as a harmful algal blooms
(HABs) and they are formed when concentrations of the phytoplankton, Karenia brevis, increase drastically (1). When these events occur, the ocean not
only turns red but it becomes an extremely toxic environment for circumambient
organisms such as dolphins, fish and humans. This blog post attempts to
integrate some of the major studies on Florida red tides and their impacts on
aquatic organisms as well as terrestrial animals such as humans.

Florida
red tides occur primarily along the west coast of Florida and the Gulf of
Mexico but have also been reported along the East coast of North Carolina (2). They
are termed “harmful” algal blooms because K.
brevis produces a suite of neurotoxins known as a brevetoxins (PbTx), which
cause acute central nervous system damage in humans and other mammals (2). Some
negative effects of HAB events include gross marine organism mortality rates,
human neurotoxic shellfish poisoning and economical disruption of the fishing
industry (2). There have been numerous studies of bottlenose dolphin mortality
events coinciding with HABs. Fish communities were also studied during HAB
events and the species richness and density were both found to be negatively
affected by the events (3). A human impact of Florida red tides is the
possibility of consuming shellfish highly concentrated with PbTx, causing
neurotoxic shellfish poisoning. Although, the correlation between K. brevis blooms and brevetoxin
poisoning may seem clear, only a small number of studies have been performed
that actually test marine animals and their communities for this toxin after
their death to determine if PbTx was indeed present.

K. brevis is a photoautotrophic dinoflagellate
that occupies a planktonic and oceanic niche with optimal growth occurring in
temperate to tropical waters (3). This microbe has two flagella, one wrapping
around the cell and the other aiding in locomotion (1). The cells are pinkish/red
in pigment, which is visible to the naked eye when their concentrations are
high enough (1). They are ubiquitously found in low concentrations in the
coastal waters of the Gulf of Mexico and Western Florida but concentrations
drastically increase during HABs. This is when marine and terrestrial organisms
are most threatened by the PbTxs (2). There are two types of brevetoxins, PbTx1
and PbTx2, each contributing a suite of derived compounds that form during HAB events
and they differ in the number of carbon rings that each contains (2). These
compounds contain a polycyclic ether ladder that binds to sodium pumps located on
neurons, ultimately altering their function and inducing cell death (2). Brevetoxins
are heat-stable as well as lipid soluble allowing for them to persist in high
saline concentrations such as those of oceans. These factors are what make PbTxs
so dangerous to the ecosystem and the surrounding life forms.

The
frequency of HABs has notably increased over the last few decades and numerous
fish kill events have been recorded in areas and times coinciding with these
events (3). Occurrences of HABs are relatively sporadic but they are though to
be primarily human induced (3). This is due to extra nutrition being added to
the oceans that the phytoplankton can utilize and thrive on (3). Geographical
location also is found to play a role in HAB occurrence (3). A study was
conducted in order to determine if Florida red tide events were in fact
affecting the surrounding fish communities, species diversity and population
densities (4). They chose a system termed; catch per unit effort (CPUE), where
they used a single large net and attempt to catch as many fishes as possible
within designated areas during HABs and non-HABs. It was found that fish
species richness and fish populations both decreased with the occurrence of
HABs but replenished when there was no such event. This indicated that K.
brevis blooms affect fish communities, their population densities and
species richness in the surrounding coastal waters (4).

Numerous
mortality events coinciding with HABs have been reported in bottlenose dolphins
where hundreds of carcasses washed up onto the shores of Western Florida and
the Gulf of Mexico (1). Samples were obtained from some of the dolphins found
and high concentrations of brevetoxins were discovered (1). Some were also
taken from dolphin prey species including different types of fish, which also contained
high concentrations of brevetoxins (1). This suggested that the dolphins were
getting sick from eating poisoned fish (1). In 1999/2000 152 bottlenose
dolphins died followed a major HAB eventand
PbTxs were found in 52% of the samples tested. In 2004 105 bottlenose dolphins died without an apparent HAB
event but all of the samples tested positive for brevetoxins in very high concentrations.
It was concluded that there must have been a HAB effecting the bottlenose
dolphin population that was not detectable with the current tools used to sense
increases in K. brevis concentrations
(1). Lastly, in 2005/2006 90 bottlenose dolphins died and 93% were positive for
brevetoxins. These records indicate that HABs of K. brevis are responsible for the bottlenose dolphin mortality
events that occurred along the west coast of Florida and the Gulf of Mexico
from 1999 to 2006.

Filter
feeders occupying a benthic niche, including mussels, clams and oysters are
prone to high accumulations of PbTx (3). This is because they continuously feed
on these toxic algae, which often settle in the benthic zone when dead (3).
Neurotoxic shellfish poisoning in humans occurs through consumption of these contaminated
shellfish (3). This directly leads to disruptions of the fishing industry and
economy by contaminating their catches and limiting productivity (3). Brevetoxins
excreted from K. brevis can also become
aerosolized through regular oceanic currents and this can cause harm to humans
and other mammals (3). Inhalation of PbTx is noted to cause burning of the nose
and eyes, a choking cough and asthma attacks (3). Despite the clear negative
effects that brevetoxins have on humans there has never been a reported death
caused by brevetoxins (3).

Current
preventative measures being taken to minimize casualties and other losses
during Florida red tide events include satellite-imaging detection, which
utilizes different mathematical algorithms to detect blooms (4). There are also
multiple types of sensors that are used to sense color changes in the ocean and
increases in K. brevis concentrations
(4). It is well known that Florida red tides are harmful events, so it is
comforting to know combative measures are being taken to prevent mass mortality
events of aquatic organisms along with human and bird brevetoxin poisoning.

Thursday, December 18, 2014

Over the past decade there has been
a growing concern over the phenomenon known as Colony Collapse Disorder (CCD)
among commercially raised and wild bees. CCD was initially characterized in
2006 by David Hackenberg, a prolific apiarist with multiple hives in Florida
and Pennsylvania1. Upon investigation of lagging production, it was
discovered that despite there being no adult worker bees in 20-30% of his hives
the queens and brood appeared healthy1. The loss of worker bees and
production from the hive while still maintaining a seemingly healthy brood and
queen has now become the definitive end result of CCD.

Since 2006, there have been
numerous investigations into potential causes but so far no single cause has
been definitively linked to CCD. Some of the more extreme claims include cell
phone radiation and commercial use of insecticides, however there is no strong
evidence to support that either is the cause of CCD1.Of the potential rational causes for CCD, the
most likely is an increased prevalence of parasites and viruses within the bee
population1. Crithidia bombi, a
recently implicated parasite, is one of the more interesting because of its
ability to infect a large variety of different bee species, including those
found within the pyrobombus, thoracobombus and bombus sensu stricto subgenera2.
Of the North American species infected, Occidentalis and Pensylvanicus are currently undergoing massive population decline
due to CCD2. C. bombi infection
is also 6 fold higher in CCD colonies as opposed to hives not experiencing CCD3.

C.
bombi is a pathogenic unicellular eukaryote with two distinct life phases;
the flagellated choanomastigote and the anchored amastigote cells4.
The amastigote cells upon ingestion will extend their flagella and swim as a
choanomastigote until they can attach to the bee’s intestinal wall and once
again become an amastigote4. Upon attachment the cell can siphon off
nutrients that pass by and will divide into new amastigote cells4.
Some of these cells will be excreted in feces and can be transmitted from bee
to bee through the ingestion of infectious cells to begin the cycle anew2,
4, 5. The amastigote cells can either be ingested within the hive,
leading to a high level of infection amongst the workers and queen, or at
flowers allowing for the parasitic colonization of new hives5. Once
within a hive, infection spreads rapidly until about 80% of the colony is
infected6. Due to C. bombi having
a genotype-genotype model of infection, in which the unique genetic profile of
the host and the parasite both play a role in infection success, the highly
related individuals within a hive are much more frequently infected7.
However, once a cross hive infection is established it will rapidly spread
within the new colony7. While infection has not been linked to any
significant lethality in otherwise healthy bees, an infected bee experiencing
starvation has a 50% increase in mortality5. Upon infection the bee
will have a harder time distinguishing between the flowers that are the most
rewarding based on color, as shown in figure 18. This suboptimal
foraging will lead to less food collection for the hive as a whole and a
potential minor starvation event that would cause increased mortality in the
infected bees8. If a queen is infected she will have reduced ovarian
capacity leading to a decreased worker population6. An infected
queen also experiences a decrease in the ability to store energy as fat for the
hibernation over winter greatly decreasing her chances of survival6.
If the queen manages to survive the winter, she will produce fewer offspring
that will also become infected6. This generational transmission pattern
is particularly vexing for apiarists because an infected queen not show symptoms
until the following year when she establishes a colony. During the time between infection and
diagnosis, C. bombi is also being
spread to nearby flowers and potentially other hives which could account for
the high infection rate in commercial colonies every year.

This continual transmission and
difficulty of removing C. bombi begs
the question, why should we care if all of the bees die? The economic impact of
the insect pollination industry is valued at over 150 billion euros9.
As shown in figure 2, this is roughly equivalent to 10% the total value of global
agricultural production9. The use of bees makes up over 70% of the
insect pollination industry and the value of crops that are been pollinated is
roughly 5 times higher than those that are not9. This is not even
considering that the apiary industry as a whole, including all of the
production facilities to manufacture bee related goods, employs millions of
workers worldwide. A shrinking of the bee population will also lead to an
increase in the cost of pollination services which will get passed on to the
consumer as a wide variety of fruits, nuts and vegetables increase in price to
compensate.

While the apiary industry is one of
the main driving forces for CCD research, the disorder is not limited to just
commercial hives. Commercial bees are commonly raised in greenhouses with a
crop to pollinate and it has been shown that a few bees escape and carry
infection into the wild10. The close confines of the greenhouse and
the fact that the bees are likely more related due to being commercially raised,
infection spreads rapidly between hives leading to a higher parasite load than
in wild bees7, 10. Any bee that escapes can spread infectious cells
out of the greenhouse and to wild bees through the shared use of nearby
flowers. Due to C. bombi’s ability to
infect a wide range of bee species, this could lead to collapse of wild bee
colonies throughout many different regions of the world. Even more worrisome,
commercial colonies are commonly transferred across the globe for pollination
purposes as well as to start up new colonies1. Therefore any
infection from a single colony has the potential to spread globally and infect
numerous native colonies. While it has been shown that a single bee proof mesh
placed over the air duct will greatly diminish the chances of escape, Commercial
bee keeping still exists as a potential method of transferring infectious
agents to native bee populations across the globe10. If the native
population of bees were to die, thousands of native plant species would lose a
prime pollinator which could lead to an inability to efficiently reproduce
devastating animal populations that rely on them for food.

Though it is likely that there is
no single cause to CCD, the research into it has turned up several interesting
parasitic species that all are likely to play a role in colony collapse. Crithidia bombi is but one of the more
interesting due to its ability to infect a wide range of bees beyond the
commercial species and infection has been correlated with CCD2, 3.
This in no way means that C. bombi is
the sole cause of CCD but that it likely contributes to the decline of affected
hives. Further research into the topic is definitely needed to determine other
contributory factors that when combined will lead to CCD. Until a large scale
prevention method is identified there are a few things that an individual can
do to help maintain local bee populations. Becoming an apiarist and setting up
a hive or two in your backyard can help provide a home for local varieties of
bees and provide a strong pollination source for nearby gardens11. Planting
a variety of species in gardens can also lead to more diverse food sources and
increase a colony’s overall health11. By supporting further research
into CCD and following through on few basic prevention methods we can hopefully
save the bee population as a whole!

The
human body has an army at the ready to attack and protect itself from invaders.
This army is called the immune system. It is equipped with weapons that span
the physical body, are effective against many different types of attacks, and
are organized in such a way that allows for strategic interactions which
amplifies the body’s defenses. When a parasite wages war on the body, the
body’s army goes into battle with full force. Winning results in successful
elimination of the parasite from the body, but may leave the immune system
weakened. Losing the battle can result in disease. Parasites have their own
arsenal of weapons, which allows them to defeat the immune system. Parasites
have mechanisms that shield them from host’s defenses and have ways to attack
specific target cells. One such parasite that wields its own sword and shield
is Trypanosoma cruzi. This motile protozoan
pathogen is the causative agent of Chagas disease.1 Chagas disease
affects the cardiac and digestive systems of the body and can cause acute or
chronic infections2.The
parasite T. cruzi uses offensive
mechanisms to counterattack a host cell’s defenses.

Chagas
disease affects eight million people in Latin America.2 The disease
was discovered in 1909 by the Brazilian physician Carlos Chagas, who named the
parasite after his mentor Oswaldo Cruz.3 Chagas disease can cause
acute or chronic infection that affects many different cells of the body.2
Clinical manifestations of acute infections include myocarditis,
pericardial effusion, or meningoencephalitis.3 After the initial
acute stage subsides, the diseases enters the chronic stage.3 Most
patients can survive with the chronic infection, but a small percentage of
patients develop cardiomyopathies within a year.3 Infection by T. cruzi occurs in a cycle and involves
blood sucking insect vectors belonging to the Reduviidae family. 4 From the insect, the parasite comes
into contact with a human or a wild animal.2 Then, it goes back to
the insect when the insect feeds off the infected human.2 When the
blood sucking insect lands on skin to feed, it also defecates in that spot
leaving behind T. cruzi infected
feces.5 Fecal droplets can get passed inside of humans through
mucosa or through breaks in the epithelial barrier.5T. cruzi can also infect through oral
transmission with infected foods.5 Another much less common
transmission mechanism is from blood transfusion.5 Congenital
transmission from infected mother to child is also possible, but like blood
transfusions is not a very common mechanism.5

Trypomastigotes
are the infectious forms of T. cruzi
and they infect the endothelial and mucosal cells of humans and other mammals.6
They invade these cells in order to differentiate and replicate inside of the
host cell lysosome and cytoplasm.6 The invasion mechanism of T. cruzi is unique because it uses the
host cell machinery that would generally be used against a protozoan parasite. T. cruzi trypomastigotes are highly
motile7. A flagellum is attached to the cell body of T. cruzi, which enables the parasite to
move on its own.8 Active motility of T. cruzi is a mechanism that the parasite uses to penetrate through
the host cell membrane.9 After it gains entry, the host cell is
infected.9 Once the host cell is infected, the trypomastigotes
undergo cytokinesis, but their nuclei do not divide.9 The division
occurs towards the back end of the basal body where the flagellum is attached.9
Through this process, the unnecessary flagellum is discharged into the host
cell cytoplasm where it is then degraded.9

The
surface of T. cruzi provides a shield
for the parasitic pathogen. This enables the parasite to travel throughout the
body without being defenseless against the host’s immune system. The major
surface components of T.cruzi provide
the parasite with protection against the host’s cell defenses and enables the
parasite to adhere to specific target cells for invasion.5 Mucin is
a glycoprotein and one of the major surface components that plays a role in
infection.1 Mucin sticks out from the outer phospholipid layer of T. cruzi’s plasma membrane.5
They are anchoredto the plasma membrane
by glycosylphosphatidylinositol (GPI).1 These GPI-anchored
glycoproteins cover the majority of the T.
cruzi’s surface.5 Mucins recognize and target endothelial cells
for invasion.5They attach
themselves onto the lipid bilayer of host cells.10 A signal is
transduced that directs the glycoprotein into the cytoplasm and to the
endoplasmic reticulum of the host cell.10 Once inside the host cell,
T. cruzi can also interact with other
organelles in the cytoplasm and use them to mediate infection.10

Host
cells have lysosomes to remove unwanted material from inside of their cells.
Normally, a lysosome would ingest, destroy, and secrete an invading pathogen.
However, upon infection, T. cruzi’s
plasma membrane fuses with the host cell lysosome, creating what is called a
lysosome derived parasitophorous vacuole.6 The formation of the
parasitophorous vacuole anchors the parasite to a structure of the host.6
The anchored parasite can undergo replication before disseminating into the
host’s bloodstream and throughout the body.6T. cruzi interacts with lysosomes of thehost cell because they have a low pH value.6Having a highly acid organelle is a
defense weapon of the host, but is used against the host when it facilitates trypomastigotes
differentiation, replication, and dissemination.6 The
parasitophorous vacuole membrane is disrupted and the acidic environment can
have its full effect on the trypomastigotes.6Disruption of the membrane is caused by the
release of the pore forming molecule TcTox from trypomastigotes.6 Release
of this molecule is triggered by the lysosome’s acid environment.6Acidity also serves as a trigger to initiate
differentiation of trypomastigotes into amastigotes.6 Amastigotes
replicate, exit the lysosome, and disseminate into the blood stream.3
This spreads infection to other cells of the body.3-6

The outcome of a battle between a
parasite and the human body is critically important. A human’s immune system is
well equipped to defend against many infections. However, parasites have
developed mechanisms that provide them with a good offense and can retaliate
against the immune system. So, in a battle between the two, the immune system
does not always defeat the invader and the parasite can conquer and win.

About Us

This blog represents the work of students from one of the few courses devoted to Eukaryotic Microbiology as a whole. This is a new experiment for this course that we hope will be a successful fusion of student learning and science communication. Enjoy, but play nice, comments are welcome but mean-spirited comments will be deleted.